The Met Office said: "Not everywhere within the warning area will see thunderstorms, and indeed some spells of warm sunshine are expected at times, but where thunderstorms do form, some torrential downpours are likely with frequent lightning, large hail and locally strong gusts.

"Significant flooding is possible where these do occur from surface water as well as from small, fast-responding watercourses. The public should be prepared for the risk of disruption from any of these elements."

There is still, however, a "yellow" warning of a heatwave for the UK today, advising people to be "alert and ready". The Met Office said there was a 60% chance of a heatwave continuing until tomorrow morning, with high levels of humidity.

John Curtin, director of incident management at the Environment Agency, said: "Intense heavy rainfall this weekend brings a surface water flood risk for England throughout the weekend. Flooding can happen very quickly and the public are urged to keep checking local weather forecasts and the Environment Agency website for information on a regular basis.

"We will continue to monitor the situation closely and support local authorities, who will respond to any reports of surface water flooding. We will also continue to monitor river levels closely and issue warnings where flooding is likely."

Ashley Williams Twitter/@thelegolawman

Lightning strike caught on camera in Swansea by Ashley Williams from the Mumbles

This picture of lightning over Swansea was taken by Ashley Williams, of Mumbles on Thursday. A church bell tower in Caerphilly county was hit by a strike causing a small fire and electricity was affected in the Pontypridd area.

The South East of England was hit by stormy weather early yesterday morning, with a reported 3,000 lightning strikes.

Gemma Plumb, a forecaster with MeteoGroup, said: "Today we have got some heavy and severe thunderstorms continuing to spread north across the UK. Most of the UK is going to see some heavy showers or long spells of rain during the day and severe thunderstorms.

"It will not be as hot as yesterday, but it will still be very warm and humid. East Anglia could still see temperatures as high as 27C (80.6F) to 29C (84.2F), Kent will see 27C (80.6F) or 28C (82.4F), rather than the 32C (89.6F) it had yesterday."

Fire crews have been called to a number of incidents caused by lightning.

The first floor and roof of a house in Sittingbourne, Kent, was set alight by a strike, while a bungalow's roof was hit in Whitstable, Kent Fire and Rescue said.

Houses were struck in the market village of Lenham, near Maidstone, while lightning also started several small fires in Willesborough, near Ashford.

A spokeswoman for Heathrow Airport said airlines were cancelling 20% of flights for a two-hour period today due to the thundery weather.

She said: "There is severe weather forecast at Heathrow with a 70% risk of thunderstorms, lightning strikes and hail storms. During thunderstorms the number of aircraft that can take off and land each hour is reduced.

"We have therefore requested that airlines reduce their flight schedule by 20% between 4pm and 6pm. Passengers due to travel on July 19 are urged to check the status of their flight with their airline before travelling to the airport."

Manchester Airport said an electrical surge caused by thunderstorms had led to some delays today.

General duty manager Gary Brown said: "It impacted on some lifts and baggage systems but most systems are now back up and running.

"We'll wait to see what happens this afternoon when we're expecting thunder."

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